saving a 1980 KZ750 twin

quick question on wiring the nuetral indicator light;
factory wiring has 12V+ to indicator light > then to neutral switch which grounds on the engine.

this wont work in my tach because the indicator light shares a common ground wire. I think I could use a relay to sort this out, but I don't want to use a big standard one. This tiny LED probably needs less than 0.5 amps. will something like this work?

https://www.jameco.com/z/EDR201A12Z-Excel-Cell-Electronics-Relay-Dip-SPST-12VDC-1A-Cont-1K-Ohm-Coil-2_106472.html

Suggestions?
 
I have this spare 20mm GSXR750 axle Id like to use. Its hollow and weighs half of what my solid ones does. The problem is its too long. The end where the threads are is swagged to 18mm. If i cut this portion off and cut 20mm threads on the main shaft I think the wall thickness will be like 1-2mm thick in the minor thread, so I don't think I can realistically do that. I'm thinking about cutting off the hex head, trimming it to length, and soldering on a new hex. I will pin the hex to the shaft as well for safety's sake. I found this solder which is very low heat (430F/221C) so I believe I should be able to solder the nut on there without removing the temper.
http://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Lead-Free-Solders/Stay-Brite-Kit.aspx

Is this a bad idea?
 

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I've done similar where I weld on the hex head plus a short length, then machine it back down clean.
 
I imagine that would work fine, presuming it is silver soldered. Keep in mind the job the axle needs to do. While it may seem that it is principally loaded in shear to keep the wheel from falling off, it is also loaded in tension. The clamping force is much more important than may be intuitively obvious. Keeping the swing arm (or fork legs), spacers, inner bearing races, and any other components tightly clamped together makes the assembly a rigid structural component that aids substantially in keeping the arm (or forks) from twisting and deforming under load. So all the mating surfaces need to be nice and square and flat, and at least as large in o.d. as the o.d. of the inner races. The larger the diameter of these parts, the greater the structural benefit. As long as your soldered joint withstands the needed clamping pressure you will be fine - so use a high content of silver. I doubt there is much special about the axle as far as heat treatment, so you should be fine heat wise. Personally I would not hesitate to simply weld it.

Looks like your little relay would be fine. Rather a pain to get the neutral light going though! Any chance you can isolate the indicator so you can power it up inside the tach and use the bikes factory switched ground?
 
jpmobius said:
I imagine that would work fine, presuming it is silver soldered. Keep in mind the job the axle needs to do. While it may seem that it is principally loaded in shear to keep the wheel from falling off, it is also loaded in tension. The clamping force is much more important than may be intuitively obvious. Keeping the swing arm (or fork legs), spacers, inner bearing races, and any other components tightly clamped together makes the assembly a rigid structural component that aids substantially in keeping the arm (or forks) from twisting and deforming under load. So all the mating surfaces need to be nice and square and flat, and at least as large in o.d. as the o.d. of the inner races. The larger the diameter of these parts, the greater the structural benefit. As long as your soldered joint withstands the needed clamping pressure you will be fine - so use a high content of silver. I doubt there is much special about the axle as far as heat treatment, so you should be fine heat wise. Personally I would not hesitate to simply weld it.

Looks like your little relay would be fine. Rather a pain to get the neutral light going though! Any chance you can isolate the indicator so you can power it up inside the tach and use the bikes factory switched ground?
If its hardened its likely to be only an anneal, and not critical in the hex end anyway. Check with a file.
 
Most forks are either clamping the axle on both ends, or the fork is threaded at one end and clamped at the other end. There doesn't have to be any force at all against the hex end. He could cut the head off completely at right length to meet the outer edge of the fork and would still work fine. The hex head is there to hold the axle while you thread the bolt at the other end. It's more a redundant retainer than anything.
 
irk miller said:
There doesn't have to be any force at all against the hex end.

With respect, this is simply not so, at least in this context. I believe this particular bike does indeed have a front axle threaded on both ends (I believe we were talking about the rear, but the parts end up functioning the same regardless of the design). It is important to understand that the axle assembly is supposed to function just like a fork brace to both stiffen the whole fork assembly in torsion (bars turn, wheel doesn't) and to keep the two forks telescoping together as a single unit. The larger the diameter of the axle (assembly), the greater the stiffness of the fork.
Indeed, you could leave the axle assembly loose and clamp it into the ends of the fork lowers. The result would be an assembly that would all stay together, but would loose very substantial strength from two sources. First, the slack in the loose threaded connections will allow motion in the assembly. This alone will impact the stiffness of the system, and cause wear in the threads that would never otherwise occur with correct assembly. But let's say there is no motion here. If that is the case, the strength of the element connecting the two legs is just the diameter of the axle itself. The correct procedure is to clamp all the components together with the axle first. This (in the main) makes the functional diameter become much larger and much stiffer, the same as a large diameter tube is much stronger than a smaller tube of the same weight. Then, when you clamp the assembly into the fork legs, you gain this very large improvement - the effective axle diameter becomes the same as the smallest o.d.sleeved component (spacer, inner bearing race, speedo drive, etc.). If the axle nuts are not tight enough, the assembly is much more flexible. The fork lowers have the clamps because there can't be any axial pressure on the fork legs. If there is, the forks will bind. This is not a factor at the swing arm, but the principles are the same otherwise.
 
jpmobius said:
With respect, this is simply not so. I believe this particular bike does indeed have a front axle threaded on both ends (I believe we were talking about the rear, but the parts end up functioning the same regardless of the design). It is important to understand that the axle assembly is supposed to function just like a fork brace to both stiffen the whole fork assembly in torsion (bars turn, wheel doesn't) and to keep the two forks telescoping together as a single unit. The larger the diameter of the axle (assembly), the greater the stiffness of the fork.
Indeed, you could leave the axle assembly loose and clamp it into the ends of the fork lowers. The result would be an assembly that would all stay together, but would loose very substantial strength from two sources. First, the slack in the loose threaded connections will allow motion in the assembly. This alone will impact the stiffness of the system, and cause wear in the threads that would never otherwise occur with correct assembly. But let's say there is no motion here. If that is the case, the strength of the element connecting the two legs is just the diameter of the axle itself. The correct procedure is to clamp all the components together with the axle first. This (in the main) makes the functional diameter become much larger and much stiffer, the same as a large diameter tube is much stronger than a smaller tube of the same weight. Then, when you clamp the assembly into the fork legs, you gain this very large improvement - the effective axle diameter becomes the same as the smallest o.d.sleeved component (spacer, inner bearing race, speedo drive, etc.). If the axle nuts are not tight enough, the assembly is much more flexible. The fork lowers have the clamps because there can't be any axial pressure on the fork legs. If there is, the forks will bind. This is not a factor at the swing arm, but the principles are the same otherwise.

You really need to read up on this more. Here is the picture he posted of the axle.

index.php


The parts do not function the same front and back. By having the bottom of the forks clamp, that is what is stiffening the front end, not having it threaded in or providing force to the underside of the hex cap. The binding of the forks onto the axle is doing the work. Notice one end of the axle in the pic does not have a hex bolt. If it were important to provide force torquing down on that, it would not be designed that way. Many, many, many axles including my BMW F650 and all modern Suzuki sport bikes are made without a cap at all.

77150-190218144314-3323524.jpeg


Here is a VZ800 front end. The axle is not capped at all. You thread the axle into the left fork and clamp with the right. There is zero force squeezing the forks together. A shoulder on the axle works against the spacers and the bearings keeping the wheel parts tight together, but the fork is separate from that force.

be1d7f1b16d02b5e591f6fcdf200e031.jpg
 
This is for the rear. I have a nice stainless axle nut that is made out of 316 I would like to use. I was a little worried about welding dissimilar metals so that's why I was thinking solder as well, but after doing some research I believe using 309L should work fine
 
irk miller said:
The parts do not function the same front and back.

Actually they DO end up the same - there are just a few extra parts needed in the front to accommodate the telescoping parts.

irk miller said:
By having the bottom of the forks clamp, that is what is stiffening the front end, not having it threaded in or providing force to the underside of the hex cap. The binding of the forks onto the axle is doing the work. Notice one end of the axle in the pic does not have a hex bolt. If it were important to provide force torquing down on that, it would not be designed that way. Many, many, many axles including my BMW F650 and all modern Suzuki sport bikes are made without a cap at all.
Here is a VZ800 front end. The axle is not capped at all. You thread the axle into the left fork and clamp with the right. There is zero force squeezing the forks together. A shoulder on the axle works against the spacers and the bearings keeping the wheel parts tight together, but the fork is separate from that force.

Absolutely agree with all of this! Evidently my communication skills are as poor as my reading ability. In all cases, the TENSION in the axle itself is important in keeping all of the various wheel assembly components together. Having these parts clamped tightly together is fundamental to how stiff this assembly is. At the rear, the swing arm is part of this assembly, so it gets clamped with all the other bits. On telescopic forks (99.99% of them anyway), either one of the legs or none of the legs is part of this assembly. (In the case of one leg incorporated, this in fact IS exactly like the swing arm situation sans one side, which obviously must be fixed independently to prevent fork bind). Either way, the axle ALWAYS has to provide clamping force. In the case of one leg being incorporated, it is clamped into the assembly and this clamping force provides the stiffness at the connection. The other end "floats" in the independent clamp on the other leg until it is tightened and this clamping force provides the stiffness there. This connection is not on the axle, but on the much larger diameter nut, which, in being previously tightened down with the wheel assembly bits effectively becomes a larger diameter axle. This of course is the same for assemblies with a nut clamped by BOTH fork legs. Once the axle assembly is tight, installation into the forks can be accomplished without tweaking the forks out of align. But the axle itself MUST clamp the wheel components together tightly first in order to maintain the structural strength of the assembly. That's the point I feel important. Sorry it took me so long to make it!

Apologies for jacking the thread - I shall work on explaining more clearly on the first pass! (as well as my reading skills!)
 
doc_rot said:
This is for the rear. I have a nice stainless axle nut that is made out of 316 I would like to use. I was a little worried about welding dissimilar metals so that's why I was thinking solder as well, but after doing some research I believe using 309L should work fine

Maybe have a look at 317L if you are determined to make one from stainless. Should be reasonably easy to get. That said, IMHO stainless steels on the whole might not be the best choice for an axle.
 
The axle, I assume, is some type of chromoly. The nut I want weld to it 316 stainless. As far as I can tell ER309L is the preferred filler rod for this application 317 seems to be for dissimilar stainless alloys. I will pin it for added safety, cause I'm a belt-and-suspenders guy when it come to this type of thing. Pro Bolt sells these nuts specifically for motorcycle axles so i can't imagine its too much of a problem.
 

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Finally had the time to cut and buff the paint. The result is dead flat with no definition line over the stripes. I also put on the badges.Ive been tinkering with the wiring off and on for months and it is finished. I did a bit of driveway tuning learned about the one year specific pilot screws to this year. Rounded up the nessecary parts and it's synced and seems to run great. All that remains to sort is an axle and a license plate. The latter of which should be here ina week or so.
 

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Thanks man. It looks even better in the sun
 
Dude. Just... dude.

This is glorious. Skills to pay the bills. Absolutely terrific looking bike, and that colour! Doing Kawasaki proud. Incredible looking bike man, massive kudos.
 
Oh yeah baby. Bikes on this forum are judged by the turmoil they cause in my Y fronts, the famous brown ones with the orange trim. Well, I can tell you they're currently stretched to the limit of the elastics ability to contain the swelling beneath, such is the pleasantness of this bike.

At first glance, utterly traditional, but a closer look reveals cleverly integrated modern detailing. Very cleverly done. One of my favourite bikes of all time too - Z1easque styling with a brawny, manly, none-of-your-new-fangled-four-cylinder-rubbish-here-son big twin motor. Love it. I want this bike soooooo bad.
 
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